asyn-ares: initial HTTPS resolve support

Gets the ALPN list the same way DoH does. Needs c-ares 1.28.0 or later.

Thanks-to: Brad House

Closes #16039

lib/httpsrr.c

@@ -0,0 +1,88 @@
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
+ *
+ * This software is licensed as described in the file COPYING, which
+ * you should have received as part of this distribution. The terms
+ * are also available at https://curl.se/docs/copyright.html.
+ *
+ * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+ * copies of the Software, and permit persons to whom the Software is
+ * furnished to do so, under the terms of the COPYING file.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ * SPDX-License-Identifier: curl
+ *
+ ***************************************************************************/
+
+#include "curl_setup.h"
+
+#ifdef USE_HTTPSRR
+
+#include "urldata.h"
+#include "curl_addrinfo.h"
+#include "httpsrr.h"
+#include "connect.h"
+
+CURLcode Curl_httpsrr_decode_alpn(const unsigned char *cp, size_t len,
+                                  unsigned char *alpns)
+{
+  /*
+   * spec here is as per RFC 9460, section-7.1.1
+   * encoding is a concatenated list of strings each preceded by a one
+   * octet length
+   * output is comma-sep list of the strings
+   * implementations may or may not handle quoting of comma within
+   * string values, so we might see a comma within the wire format
+   * version of a string, in which case we will precede that by a
+   * backslash - same goes for a backslash character, and of course
+   * we need to use two backslashes in strings when we mean one;-)
+   */
+  struct dynbuf dval;
+  int idnum = 0;
+
+  Curl_dyn_init(&dval, DYN_DOH_RESPONSE);
+  while(len > 0) {
+    size_t tlen = (size_t) *cp++;
+    size_t i;
+    enum alpnid id;
+    len--;
+    if(tlen > len)
+      goto err;
+    /* add escape char if needed, clunky but easier to read */
+    for(i = 0; i != tlen; i++) {
+      if('\\' == *cp || ',' == *cp) {
+        if(Curl_dyn_addn(&dval, "\\", 1))
+          goto err;
+      }
+      if(Curl_dyn_addn(&dval, cp++, 1))
+        goto err;
+    }
+    len -= tlen;
+
+    /* we only store ALPN ids we know about */
+    id = Curl_alpn2alpnid(Curl_dyn_ptr(&dval), Curl_dyn_len(&dval));
+    if(id != ALPN_none) {
+      if(idnum == MAX_HTTPSRR_ALPNS)
+        break;
+      alpns[idnum++] = (unsigned char)id;
+    }
+    Curl_dyn_reset(&dval);
+  }
+  Curl_dyn_free(&dval);
+  if(idnum < MAX_HTTPSRR_ALPNS)
+    alpns[idnum] = ALPN_none; /* terminate the list */
+  return CURLE_OK;
+err:
+  Curl_dyn_free(&dval);
+  return CURLE_BAD_CONTENT_ENCODING;
+}
+
+#endif